In connection with the production of a membrane for an electroacoustic transducer and specifically for a loudspeaker, for example for small loudspeakers for mobile telephones, it is known, in the case of currently available membranes produced for example by means of a deep-drawing process, that although increasingly high acoustic pressures are to be generated, the membrane tends to buckle during operation if such a loudspeaker is small, on account of the thin, film-like structure of the membrane and on account of a relatively flat membrane cup, and this can be perceived acoustically by a user of the mobile telephone and is disruptive and unpleasant. The aim is therefore, even when using thin membranes formed for example by deep-drawn plastic films, to make at least part-areas of such a membrane more rigid in order to provide the necessary strengths even in the case of small membranes for a loudspeaker. In the membranes available to date, which are produced by means of a deep-drawing process, it has not been possible in the case of the desired small size to achieve the necessary rigidity in particular for producing a hard membrane center or membrane cup. Moreover, when producing a membrane for a loudspeaker by means of a deep-drawing process, it is impossible or not readily possible to give the membrane different rigidity properties in different part-areas, for example by virtue of different material thicknesses.
In connection with the production of membranes for loudspeakers having different rigidity properties or material properties, it is known for example from the patent document WO 89/00372 to produce a multilayer membrane, wherein a second plastic film is applied to a first plastic film provided for stabilizing the shape, in order to achieve desired damping properties in respect of partial vibrations. Not only is the production of such a multilayer membrane extremely complicated, but there is also the problem that the films which are to be arranged above one another or applied to one another have a constant material thickness over their entire extent and thus have constant material properties, so that once again in this known design it is not possible to produce a membrane comprising part-areas with different material properties.
In connection with a method of producing a membrane for a loudspeaker or an electroacoustic transducer, it is also known from the patent document AT 403 751 B to fix part-areas of a membrane in a multistage production method and to subject other, non-fixed part-areas to thermal and/or mechanical stress, in order thereby to obtain part-areas with different material thicknesses of the membrane and thus different material properties. This method, too, is disadvantageous in that extremely complicated method steps are required during production.